Project 1: Abstract Rice (Oryza sativa), a staple food for over half the world's population, represents a significant dietary source of inorganic arsenic (As), a non-threshold, class 1 human carcinogen. It is imperative that strategies to reduce grain As are developed, and establishing the mechanisms that enable As to reach and accumulate within the rice grain is key to this endeavor. This project will elucidate the genetic control of As homeostasis in plants to enable the development of plants that do not accumulate As. The first specific aim tests the hypothesis that genetic diversity in rice can be exploited to lower grain As levels by mapping genes in accessions known to vary in grain As content. The second aim asks more generally what genes are involved in transferring As to the grain and the third aim tests strategies to limit the movement of As to the shoot/grain based on information gained from study of rice, Arabidopsis and the As accumulating fern Pteris vittata. The long-term goal is to prevent As accumulation in the edible portion of rice grain, but the work will also potentially provide information on genes responsible for transporting As and other contaminant metal(loid)s into the tissues of other edible plant organs. In addition to identifying the causal loci, synchrotron X-ray fluorescence microanalysis (SXRF) will be used to precisely localize and speciate As in plants, an innovative approach that has been used successfully to examine seed loading of As.